Variable electrical trimmer capacitor



' Aug. 13, 1963 s l 3,100,856

VARIABLE ELECTRICAL TRIMMER CAPACITOR Filed March 1:5." 1961 INV EN TOR.

A TTOANEYS of the capacitor.

tages.

3,100,856 VARIABLE .ELECTRECAL TR? Llewellyn-T. Barnes, 1155 Atlanti 1 t Filetl'Mar. 13, 1961,;Ser, No; 95,191 5 Claims. (Cl; 317 249),

My invention relates to variable electrical. capacitors and. specifically to capacitors of the trimmer't ype which are used to produce precise capacity variations.

The present invention is a continuation-inputof .my

[. .copending application Serial nogsznas, filed October 112, 196i}; for Economy Piston Capaciton- In y aforementioned United States patent applicanon, S'erialNo. 62,295, I have disclosed a trimmer ca-' paci t or of the type in which a piston" constituting a movable electrode is slidablewithin acylindrical body Freeport, NY. 7

UnitedstffisPateflt {0 7 tion. of back-lash is springs.- a .A further object of the invention is to provide a trimmeratype piston capacitor which is composed of few han icev

accomplished Without the use of parts, is simple to construct and assemble, lends itself to mass production techniques, and at the same time is ellective to prevent rotation of the piston. 4 Additional objects and advantages, of the invention will become apparent duringthe course of the following specification when taken in connection with the acvco'rnp-anying drawings, in which:

' t FIG. 1 is a longitudinal sectional view of a capacitor made 'in accordance with the invention; and, i 7 FIG. 2" is atransverse section taken along line 2-2 of Y With continuing reference to the drawings, wherein.

made of dielectric material andhaving an,external.con'- tive tothe cylinder coating, thereby changing the capacitance ofythe. unit. An anti back-lash mounting is supplied for. the adjustingjmemberin the nature ofa gductive coating constituting the fixed electrode or plate 1 The piston'h as an internally threaded bore. which receives the threaded end of la rotatable adjusting member in such amanner that whenthe adjusting member is rotated, the piston is rnoved, axiallyrelainvention and having a frontjend bushing 12. The .busliih'g'lZ is formed with a central aperture 'Mconiniunicating with an inner bore orchamber' 16, bushing 12 also has a chamfered ortape'red inner surface 18 adjlace'nfaperture lifor a reason hereinafter 6X5 plained. Bushing 12 is also provided with front circum- ,ferential flange 26 from which projects a tubular portion spring exerting outward pressure on the adjusting memherin such a manner asto maintain the threaded con-x neotion under constant tension. f

.- The use of a spring to provide,isuificient tension to eliminateback-lash has been found effective operaadverse weather conditions. r g

It is an object or the pre tion, but has also presented several practical disadvan- The springs themselves are relativelyfcostly and increase the over-all .manufacturing'cost. of the nnit. Further, their tension is affected during continuousj 'use and" they are subject to breakageundenheavy use and I invention to provide a mimme pacimr of the type, described in whichanalteii nate means, is provided .to lproducej fa bias ingpforce on the adjusting member and .toprevent baclc-las'h, thereby eliminating the use offsprings for thisjpu'rpose.

In accordance, with ',the present invention, there {15 i provided a piston (trimmer, typeficapacitor having a cylindrical "body, one high dielectric material; An 'ad g j usting rriembenfwhich. isthreaded for only a small ,iiendof' the;piston is attachedrtoia' wa en'having asqu I apertu re which coa'cts with a; squareprojeotion linder ancl thereby prevent th 4 ffl t i 195133 93 din ,One of the; objects -of the invention 1s; to. piovide a pistonjtype trimmer capacitor of the character described which requires a minimum of machiningito-produce. V y it Another objectof the invention is t'oproyide aPistontype trimmer capacitor of-the character described which is extremely economical in manufiaoture in that elimina- Mi i gtd .generally "by",reference numeral 28 and comprisinga.cylindricaLshankQtD terminating at one end in an enlargedithieaded portion 32." The other end of onjthe cylindersurface and then fired;

nbneondnctive mate FIG. 2.

7 like reference numerals designate similar partathere is shown a capacitor "it? made in accordance with the 22 of reduced, diameteriand defining the inner bore in. A hollow cylinder 24, made of a dielectric material such as quartz, glass, fTitania or the like, is rigidly and,

concentrically attached to the bushing =12. A band 25 0f afconductive metal such as silver, is fitted about the 'outersurface of cylinder .24 adjacent the rear end thereof,

and isjsecured to said cylinder. outer surface, as'by cementing. Asian alternative, the band may be sprayed The/capacitor in also includes an adjusting member ,shankjfiii'carries anlintegral terminalhead piece 34;. The

IheadLpiece' 34'hasilataperingiinner portion 36 which is xcornplementary to the tapered surfacelti ot'bushing 12' -adjacentaperture .14. a In assembly, the bushing 12 can slid into thejfrontend of hndet-Qdlyvdth.the head hrough the" bushing bore ldiuntil tapering por-tion 36 bushing 12.

Xteriorly of the dielectric Wall ofjcyliny by" referencenu-meral 38., Eleccylindrical metal piston 4tthaving central threaded. to

fi fi b pey te W '4 i PrW quarecentralapertureda whicthreaded Q 'tightly fitted within the rear openend of cylinder" '24, and

cementedin place. The .endcap 48 is providedjgv ith an integralinwardly-projecting postSli of square cross' sec-f' tion; Post 5% is sized to closely fit within the square j'apert'nrevenfofwasher 44-. Thus','w-hile washer 44 can Patented Aug. 13, 19%3 The tubular'portion 22 of bushing 12 is inserted within the'front open end of cylinder 24- and is secured therein asbycementing-with the end oif ncylinder 24 abutting hange -'20 and chamber l6 cornnrunioating with the in terior j'offlcylinder 124. Y

ece. 34 of the mounted adjusting member z passin'g head piecesi'nt is seated, upon-the, tapered surface 18 conduct ebafnd. 'iistitutesafinedielectro d e of i V apacitorl'i fl also includes a movable elec-,

rider l lalongtheiinner surface 2-, and alwas'her is, madam portion 32 of shank 30, the slot 52 permitting a'slight provided with a 'kerf or slot 64 for facilitating the rotation "o fthelf tension screw 56 and hence the position of the bearing58. Thus, a screwdriver orsimilar'tool may be 1 Linserted through the rear open end of bore 54 until it engages thekerf not tension scre'wSd. The'tension screwv 56 can then be manually adjusted until thejproper tension is provided against the adjusting'member threaded end portion 32.

v ing of the bore 54.-and its contained tension screw 56, and because of the point contact provided by the tip-j58 of Q produce a corresponding rotation of tension screw 56. Screw 56, rather, .willtend to remain immovable.

V j 4 member 28 are made of a; conductive metal :haS"

an extremely lowcoefiicientfiof. thermalexpansion.

' Inland isithusfelectrically"connected-to piste-r1 10 through; fltheconductive adjustingmember28. A ring or rings'70" V therewith.

slide along'post 5t), neither washer 44 nor the piston 40- carried thereby can rotate relative to post St) or cylinder 24. Electrode 38 therefore is constrained to move longitudinally through cylinder 24 without rotation therein A keyhole-like slot 52 is provided in the threaded end 5 deformation in the length of said threaded end portion 32. The end of the threaded end portion 32 normally abuts the facing end of the square post 50. s

The square post 5%) is provided with an internally threaded bore 54 which is threaded in the opposite direction of the internal threaded bore 42.. A tension screw 56 is threadedly engaged in the threaded bore 54. The tension screw has a conicalor pointed tip .58 at'the inner end thereof facing the threaded end portion 32 of shankf 30. The pointed tip 58 forms a hearing or pressure point :and seats in a conical depression .60 in thefend face 62' of ththrfeaded end portion 32 of shank 30 in bearing, engagement. The opposite end of the tension screw 56 is.

Under pressure oftension screw 56, the sections of the threaded end por tion 32 are pressed together, bringing the external threading slightly out of alignment with the meshing internal threading42 of piston 40, and thereby creating a drag on this screw threading. This tensioned drag serves to provide smooth, uniform and fine adjusting movement or the piston .40, and also holds the latter in precise adjusted position at all timesQeven whensuhjected tojarring, vibration or the like, and also eliminating back-lash and creepage. Because of the reverse threadsaid screw 56, rotation of adjusting member 28 not 40 The forward end ofhead piece' 34 projects slightly.

outwardly from the bushing, a ert sm and is provided with a kerf 66 .at the outer end-thereof for the reception of a screwdriver 'or similar bladed tool which may be used to (facilitate the rotation thereof.during adjustment. 1

stitutes the fixed electrodeof the capacitor'lilgfifThei band.

26 and electrode 38 are separated by' the body of cylin' der i- 7 2 4 which has arhigh dielectric constant. capacitance of the unitis changed rotating adjustingTscrewf 28, th

- rotation being translated S into longitudinal movement ff 1 piston 4 0 co-nstituting movable'electrode filil relative 't't) fixed band 26. 'IThe movable "electrode 38 receives cits 6 charge; through. terminal 68, Jbushing? :12 and adjusting member ass The engaging lt'aper'in surfaces- 18 of the 1 bushing-1 2; and surface 3 6 of'gthe headpiece .34 provide 7 good electrical contact hetweenjthebushing 12 andthe I adjustingmember 28,;Iunder the .biasing force of tension" s r ws In theposrtion of the capacitor shown-in FIG. 1, the

j g piston 'd'flis in registry with the fixed electro-de band zd,

constituting a position f-of maximum capacitance. when.

p the shankfill isrotate-dby'nianual' turning of the head-lpie'cef34,the piston 49 travelsdn a'righthand direction capacitor is capable of being more economically :manu factured than was heretofore feasible. 7

' preventing rotation of stride-piston elec'trodeexte long tud nally throughv the bore. of js'aid-piston'electrode andengagingsaid terminal portio'n of sa'ild shank for ,55 i terniinalportion of saidshank lis maintainedjn tight formedofa 'material having a high f dielectr'ie constant,

e d fisa ylin r e lure. communicating Withthefinterior or said' cylin 1 an; adjusting j member extending frotatably through said bushingaperture; said V I locatedfcutside said bushingjashank and :ext ,n'd' g; longitudinallyand, centrally int ton electrode slidahlein' said cylinder jandhavin'g ac vminal member having a non-circular. .aper'tureinjcom munlcation with said threaded bore, and an end ca'p s'e cured .to the other end of, said cylinder opposite saidv 75, bushing. and having a longitudinally-extending post of I asviewed in FIG. 1, away from the band 26, and the'area of registry of the electrodes gradually decreases until the rear edge of the piston 40 reachesthe forward (or righthand) edge of the band 26, constituting the position of minimum capacitance. To permit such position to be reached, the washer i4 is cupped or depressed at its cen- I ter, as indicated at 74, this depressed central area providing clearance about the shankt-hreaded end portion-32 y when the piston it? approaches its position of minimum' capacitance. Also thetorward portion of piston 40 is provided with a reduced diameter, indicated at '76, which Y the within the bushing borelld in the position of minimumv capacitance. Thus, itis seen from the above description, theonly' pieces of capacitor 10 which require extensive machin'-,x ing are the threaded portion 32, ltension screw 56. and 1 internally threaded piston 40 and square extension 5 0.

The complete unit is easily assembled with a V of cementing and soldering.- Thus, production costsand assembling costs are considerably decreased and ,the

It will be noted that the novel construction of the piston 4t) and washer 4 5 permits the piston to travel'between a position of complete registry with thefixed electrode or band 26 and a position wholly out of registry with said band26, while at the same timekeeping the length of the cylinder 24 to a minimum. Thus, a trimmer capacitor of exceptionally small lengthfis provided fioruse with miniature electrical units or the like.

While a preferred embodiment of the invention has be n I shown and described herein, it is. obvious that numerous 1 7 changes, additions and omissions may be made in-such" embodiment without departing from the spirit and scope of the invention. 'What I claim is:

l. A trimmer capacitor comprising a hollow cylinder 1 'formed of a material having a high dielectric constant, an.

adjusting member rotatably mounted in said cylinder and including a shank extending axially into the interior of. said -cylinder, an externally-threadedterminal portion :at the; end'of said shank andhaving a slottherein for defolimation. of the external threading thereof, a piston elec trode slidable in said cylinder; said-piston electrode having V aninternally-threaded, longitudinal through borereceiving the threadedterrninal portionof' said shank, means 1 I for. preventing rotation of 'said piston electrode within a I said cylinder so that s'aid piston electrodeislmoved lofigif tudinally throug hsaidcylinder whn said. shank is r otated, and adjustable means carrie'd by saidfjmeans'for' forming 'saidterminal portion otsaid shank so'that s d norm, engagement with said piston electr'ojd' bushing friction allyinterfit rwithiand closin" off iusring'm m e h vin carried bysa terior :bf said cylinder, and Jan.externallyfihreaded. ter

minal 'p'or'tion at theIe'nd-ofsaid'ishankfa cylindrical tralint ernally tlireaded through-bore receiving thegthreadedterminal portloii of said sha'nlg'said piston carlryingaite non-circular cross-section, said post slidably receiving the non-circular aperture of said terminal member and extending through the threaded bore of said piston and in abutting relationship with said terminal portion, said post preventing rotation of said piston electrode within said cylinder so that said piston electrode is moved longitudinally through said cylinder when said shank is rotated.

3. A trimmer capacitor comprising a hollow cylinder formed of a material having a high dielectric constant, a bushing frictionally interfitting with and closing oif one end of said cylinder, said bushinghaving a through aperture communicating with the interior of said cylinder, an adjusting member extending rotatably through said bushing aperture, said adjusting member having a head located outside said bushing, a shank carried by said head and extendingforwardly into the interior of said cylinder,

,and an externally-threaded terminal portion at the forward end of said shank, a cylindrical piston electrode slidable in said cylinder and having an internally-threaded through bore receiving the threaded terminal portion of said shank, said piston carrying at its forward end a member having a non-circular aperture in communication with said threaded bore, and an end cap secured to the forward end of said cylinder opposite said bushing and having a post of non-circular cross-section extending longitudinally through-said threaded bore toward the threaded terminal portion of said shank, said post fitting slidably within said non-circular aperture and preventing rotation of said piston electrode within said cylinder so that said piston electrode is moved longitudinally through said cylinder when said shank is rotated, the terminal portion of said shank being slotted for deformation thereof, and adjustable screw means carried by said post engaging said terminal portion of said shank for deforming said terminal portion of said shank so thatsaid terminal portion of said shank is maintained in tight frictional engagement with the internally threaded bore of tension screw on said terminal portion deforms said terminal portion to maintain said terminal portion in tight frictional engagement in said bore in said piston electrode.

5. A trimmer capacitor comprising a hollow cylinder formed of a material having a high dielectric constant, a bushing frictionally interfitting with and closing off one end of saiid cylinder, said bushing having a through aperture communicating with the interior of said cylinder, an adjusting member extending rotatably through said bushing aperture, said adjusting member having a head located outside said bushing, a shank carried by said head and extending into the interior of said cylinder, and an externally-threaded terminal portion at the end of said shank, a cylindrical piston electrode slidab'le in said cylinder and having an internally-threaded bore receiving the threaded terminal portion of said shank, said piston carrying a member having a non-circular aperture end cap having a post of a non-circular cross-section, said in communication With said threaded bore, and an end cap secured to the other end of said cylinder opposite said bushing and having a longitudinally-extending post of non-circular cross-section, said post fitting slidably within said non-circular aperture and preventing rotation of said piston electrode Within said cylinder so that said piston electrode'is moved longitudinally through said cylinder when said shank is rotated, said post having an internally threaded bore threaded in the opposite direction to said bore in said piston electrode, a tension screw secured in said bore in said post and engaging said terminal portion, said terminal portion having a key-hole slot therein so that force exerted by said tension screw on said terminal portion deforms said terminal portion to maintain said terminal portion in tight frictional engagement in said bore in said piston electrode.

References Cited in'the file of this patent UNITED STATES PATENTS Germany Jan. 4, 1944 

1. A TRIMMER CAPACITOR COMPRISING A HOLLOW CYLINDER FORMED OF A MATERIAL HAVING A HIGH DIELECTRIC CONSTANT, AN ADJUSTING MEMBER ROTATABLY MOUNTED IN SAID CYLINDER AND INCLUDING A SHANK EXTENDING AXIALLY INTO THE INTERIOR OF SAID CYLINDER, AN EXTERNALLY-THREADED TERMINAL PORTION AT THE END OF SAID SHANK AND HAVING A SLOT THEREIN FOR DEFORMATION OF THE EXTERNAL THREADING THEREOF, A PISTON ELECTRODE SLIDABLE IN SAID CYLINDER, SAID PISTON ELECTRODE HAVING AN INTERNALLY-THREADED, LONGITUDINAL THROUGH BORE RECEIVING THE THREADED TERMINAL PORTION OF SAID SHANK, MEANS FOR PREVENTING ROTATION OF SAID PISTON ELECTRODE WITHIN SAID CYLINDER SO THAT SAID PISTON ELECTRODE IS MOVED LONGITUDINALLY THROUGH SAID CYLINDER WHEN SAID SHANK IS ROTATED, AND ADJUSTABLE MEANS CARRIED BY SAID MEANS FOR PREVENTING ROTATION OF SAID PISTON ELECTRODE EXTENDING LONGITUDINALLY THROUGH THE BORE OF SAID PISTON ELECTRODE AND ENGAGING SAID TERMINAL PORTION OF SAID SHANK FOR DEFORMING SAID TERMINAL PORTION OF SAID SHANK SO THAT SAID TERMINAL PORTION OF SAID SHANK IS MAINTAINED IN TIGHT FRICTIONAL ENGAGEMENT WITH SAID PISTON ELECTRODE IN SAID INTERNALLY-THREADED BORE. 